Apparatus for sea life locator



Sept. 16, 1969 M. J. EREBISH ETAL 3,466,753

APPARATUS FOR SEA I JIFE LOCATOR Filed Dec. 9, 1966 4-Sheets-Sheet. 1-

I BY

INVENTOR ATTORNEY Sept. 1969 M. J. PREBISQ 'ETAL 3,466,753

APPARATUS FOR SEA LIFE LOCATOR Filed Dec. 9, 1966 4 Sheets-Sheet 2 INVENTOR Michael J. Prebl'sh Hurley EQHoIt ATTORNEY p 1969 M. J. PIREBISH 'ETAL 3,466,753

APPARATUS FOR SEA LIFE LOCATOR File d Dec. 9. 1966 4 Sheets-Sheet 5 INVENTO S MICHAEL J. PREBISH BY 'HARLEY E. HOLT ATTORNEY pt. 16, 1969 M. J. PREBISH ETAL 3,466,753

APPARATUS FOR SEA LIFE LOCATOR Filed Dec. 9, 1966 I 4 Sheets-Sheet 4 INVENTORS MICHAEL J. PREBISH BY HARLEY E. HOLT ATTORNEY United States Patent 3,466,753 APPARATUS FOR SEA LIFE LOCATOR Michael J. Prebish, Adelphi, Md., and Harley E. Holt, Arlington, Va., assignors to Singer-General Precision, Inc., a corporation of Delaware Filed Dec. 9, 1966, Ser. No. 600,634 Int. Cl. G01c 21/20; Gtllb 3/14, 5/24 US. Cl. 33--1 Claims ABSTRACT OF THE DISCLOSURE This disclosure describes a bridge for use with a multirecord recorder to generate electrical signals proportional to times that variations in the individual records occur. The recorder uses a single record receiver which moves with time and a plurality of pens to make a plurality of records. All of the records represent the same information supplied from separate, spaced transmitters. The bridge spans all of the records and comprises a manually movable hair line for each record. Drive means is provided to drive the bridge in synchronism with the record receiver. Ore station serves as a reference and its hair line is moved to an anomaly in the recording with the bridge moving in synchronism with the record receiver. The hair lines at the other stations are then moved to the same point on their respective records. Electrical signals from the individual transducers then represent the movements of their resnective hair lines.

RELATED APPLICATIONS This invention relates to the invention disclosed in the copending patent application Ser. No. 514,525 of Michael Prebish, filed on Dec. 17, 1965, now Patent 3,388,373 and entitled Sea Life Locator, and is an improvement thereover.

BACKGROUND OF THE INVENTION This invention relates to a sea-life locator, and more particularly to a system for readily displaying the location of sources of under-sea sound signals which are remote from the display device.

One of the problems which has plagued modern man in many of his activities has been the ready identification of the position or location of a source of signals. This is true in connection with artillery fire where the source of a sound is located, and it was equally true during the pioneer days in North America when the hunter would try to locate his quarry by means of the sound the quarry made. As the distance over which the communication was received increased, the distance at which a positive identification of the location of a signalling object had to be made also increased. This became particularly true when navigational instruments were being devised for the more modern high-speed transportation systems which range far and wide. Radio beacons may be used as markers to indicate to aircraft in its vicinitiy the location of the beacon. However, this information may be utilized only if the pilot of the aircraft can locate his ship with respect to the beacon. Thus, even though the beacon transmits a unique signal which is characteristic of that beacon only, the beacon location may be known but the aircraft location is not, unless the relative position of the two are known.

In the past, one effective way in which the locations of distant signal sources were determined was by triangulation where a signal from a source was received by a plurality of receivers and the bearing between each of these receivers and the source was noted. The intersection of the charted bearings from each of these receivers then 3,466,753 Patented Sept. 16, 1969 indictaed the signal source. However, triangulation is a system which can be used only when a plurality of directional receivers at different locations are available. When a single receiver is used to identify the location of a remote signal source, other means must be provided.

Another system of locating under-water sound sources has been developed for use in water where the identification of the location of sea life such as schools of fish is desired. In this system, several under-water listening devices are arranged to pick up under-water sounds from a sound source and to transmit, by radio, the signals which are picked up to a single position, preferably a multi-channel radio receiver or a plurality of radio receivers. At the receiver position, the sounds picked up by the listening devices are plotted on charts or are otherwise utilized to locate the location of the sound source with respect to each of the listening devices. If the position of the receiver with respect to each of the listening devices is known, then the location of the source of sound, such as a school of fish, with respect to the receiver position is also known. This system is useful in fishing fleets for locating a school of fish readily and accurately to assure a good catch and to save time. The under-water listening devices, which are located on each of the ships in the fleet may be standard acoustic depth gauges, Sonar devices, or the like, in which the output from the sound transducers may also be coupled to the radio equipment normally carried on board the ship. Thus, the acoustic transducers produce outputs in accordance with the sound received through the water by them and this output is used to modulate the radio equipment on board the ship. This system may also be used as a rapid means for locating ships or airplanes in water which are in distress, and similar water-borne devices.

In the past, the implementation of a system of this nature usually required a substantial amount of time. The information was received from each of the under-water listening devices and the received information was, in turn transmitted to a single receiver position. The location of the listening devices with respect to the receiver position was manually plotted on charts. The information received by the listening devices and transmitted to the receiver position was also recorded graphically. Then, templets or other suitable devices were used on a trial-and-error basis to locate the sound source on the charts.

SPECIFICATION It is an object of this invention to provide a new and improved system for locating signal sources.

It is another object of this invention to provide a new and improved apparatus for rapidly and efficiently deter.- mining the location of a source of signals with respect to a plurality of signal transducers.

It is a further object of this invention to provide a new and improved system for rapidly and accurately displaying the relative locations of a source of signals and a plurality of transducers which respond thereto.

It is still .another object of this invention to provide a new and improved system for rapidly, efficiently, and accurately displaying the relative positions of .a receiver and a source of signals.

Other objects and advantages of this invention will become more apparent as the following description proceeds, which description should be considered together with the accompanying drawings in which:

FIG. 1 is a pictorial illustration of the sea-life locator of this invention as it is used by a fleet of fishing vessels to locate a school of fish;

FIG. 2 is a graphical illustration of the method by which the system of this invention operates;

FIG. 3 is a pictorial illustration of the equipment used in this invention;

FIG. 4 is a plan view of a portion of the recorder of FIG. 3 showing the bridge of this invention;

FIG. 5 is a side view of a fragmentary portion of the apparatus of FIG. 4;

FIG. 6 is a perspective view of the entire bridge showing four stations;

FIG. 7 is a perspective view of the gearing in each bridge station; and

FIG. 8 is a perspective view of the carriage member which carries the hair line.

Referring now to the drawings 11 detail and to FIG. 1 in particular, the reference character 11 designates a school of fish, which, in this discussion, is the source of signals to be located. Three fishing vessels, 13, 14 and 15, are shown at the surface 12 of a body of water such as one of the oceans. Hanging beneath the individual ships 13, 14 and 15 are under-Water listening devices 16, 17 and 18 respectively. Antennas 22, 23 and 24 .are mounted above each of the ships 13, 14 and 15 respectively to transmit radio signals from ships 14 and 15 to ship 13.

In operation, when sea-life is suspected to be present in the general neighborhood, ships 13, 14 and 15 listen in. The positions of each of the ships 13, 14 and 15 are known to each other, and each ship comprises a sound head or transducer 16, 17 or 18 which responds to the reception of sound signals transmitted through the water 12 from the fish 11, and which generates electrical signals in response to the reception of the sound signals. In addition, both ships, 14 and 15, contain radio transmitters having preselected frequencies of transmission. The outputs of the sound heads 17 and 18 modulate the radio frequency signals generated by the respective transmitters and the resulting modulated radio signals are transmitted into space by the antennas 23 and 24 to be received by receivers on the ship 13. In the ship 13, the received modulated radio signals from ships 14 and 15 are demodulated and the resulting modulating signals are recorded on charts or recorders. The receiver contained on board ship 13 is a multi-channel receiver and receives the radio transmissions from both of the ships 14 and 15. Since each of the ships 14 and 15 has its own frequency of transmission, the receiver on board ship 13 must separate each of the signals from the others. Then each is demodulated to produce an output which is recorded.

Normally, the sound emitted by the school of sh 11 remains fairly uniform over substantial time intervals so that the recording made from the signals received by the listening devices 16, 17 and 18 appear to be the same. However, periodically, a change will appear in the pattern of the received sound signals. The fish may change speed or course, or another action will occur which will interrupt or change the pattern being recorded. Since the ships 13, 14 and 15 are not all the same distance from the school of fish, the times at which the break in the sound pattern reaches the different ships will vary. Thus, on the recorder charts in the ship 13, the break in the pattern will be recorded .at different times. In FIG. 2, the school of fish is identified as the marked 11 and the ships 13-15 .are shown spaced about the fish 11 at different distances. With signals received from the fish 11, at times which are proportional to the distances of the ships 13-15 from the school 11, it is possible to determine the position of the school of fish 11 with respect to the ships 13-15. The differences in the times of receptions of the signals by the ships 13 and 15 from the reception of the same signals by the ship 14 are determined graphically. If, as mentioned above, a recorder is used to chart the signals from the ships 13-15, then the differences in the times of the signal receptions can be determined by simple subtraction from the chart. The three ships are located on a chart as shown in FIG. 2. Then a circle representative of the diiferences in the times of reception is drawn about each of the ships locations. For ship 13, the circle is 31; for ship 15, the circle is 33. Since the difference in the time of reception of the signals received by the ship 14 from the time of reception of the signals by the ship 14 is zero, no circle, or a circle of zero diameter is drawn about the ship 14. Then, the diameters of the circles about all three of the ships 13, 14 and 15 are increased by the same amount, and new circles are drawn until all three of the circles intersect. This is the location of the school of fish 11 with respect to the ships 13-15. The first layer of trial circles in FIG. 2 are designated 34, 37 and 41 and they are the same amount larger in diameter than the next smaller circle about the individual ships. Then, the circles 35, 38 and 42 are drawn. This process is continued until the circles 36, 39 and 43 are drawn. These three circles intersect at the point 11. The signal source may also be determined by using a transparent over-lay of concentric circles to find .a given circle which will be tangent to circles 31 and 33 and pass through circle 14 (circle 14 has a zero radius). The center of this given circle 44 represents the signal source 11.

The above-described methods for determining the location of the sound source with respect to the three sound transducers work Well, but they are time consuming and subject to many sources of error. Each measurement is a potential source of error as is each circle drawn. To avoid these errors and to shorten the time required to determine the location of a sound source, the equipment illustrated in FIG. 3 was devised. This equipment comprises a chart recorder 51 having a suificient number of markers to accommodate the necessary number of ship signals and having a record receiver 52 moving in proportion to time, and a bridge which carries specialized apparatus to be described below. A selector switch device 55 for selecting which of the charts are to be monitored and including manual selector knobs 56, 57 and '58 is connected to the chart recorder 52 and to a cathode ray oscilloscope 61. A second switching device 62 is coordinated with the switching selector 55 and comprises manual selection knobs 63, 64 and 65 and is connected to the oscilloscope 61 also. The operation of this equipment will be explained, in connection with FIG. 6.

The chart recorded 51 may be any standard chart recorder in which the paper, or record received 52 is driven with respect to time. In addition, the recorder 51 must include at least three recording pens or markers. Preferably, the markers are of the type that make an excursion across the paper '52 and contact the paper at the beginning of a record and leave the paper at the end of the record before returning for the next stroke. However, any suitable recorder may be used including galvanometer operated pens, helix and drum recorders, etc. To accomplish the measurement of the time differences between the reception by the individual listening devices of the same signals from a desired sound source, a bridge 54 is added to the standard recorder. The bridge 54 is shown schematically in FIGS. 4 and 5 but in more detail in FIGS. 6, 7 and 8. Assuming for this discussion that the chart recorder 51 comprises a bed over which a chart 52 is driven with rspect to time, and includes a plurality of markers for marking information on the chart 52, the bridge 54 is constructed to pass over the chart 52 and the markers. The bridge 54 should be arranged to extend at right angles to the direction of movement of the record receiver 52 as it is shown in FIG. 3. In FIG. 4, the record receiver 52 is shown with information recorded thereon in the form of three separate recordings 67, 68 and 69, and with the bridge 54 supported on racks 66 mounted on either side of the recorder 51 by means not shown so that the bridge 54 extends across all of the recording-s. Since the markers may be any type of conventional markers, they have not been shown in these figures. The bridge 54 may comprise for each record position a counter 71, 72, 73 and 74; a control knob 75, 76, 77 and 78; and a hair line mounted on movable supports 81, 82, 83 and 84. The designations t t and t represent times that an interruption to the normal recordings occurred. In FIG. 5, the side view of a portion of the recorder 51 shows the rack 66 and the drive pinion 91 for moving the bridge 54. The pinion 91 is driven by its own motor, not shown, or by the same motor that drives the record receiver 52 through a clutch of suitable design. Mounted on the bridge 54 are hair lines 85 which are positioned over each of the recordings 67, 68 and 69 and which are each supported on a movable plate 79. The plates 79 also carry mirrors 89 attached to the supports 81, 82, 83 and 84 so that an observer may view the hair lines 85 and the recordings 67- 69 easily. Or, the hair lines could be thin lines of light projected on the chart, and prisms having scales etched thereon can be substituted for the mirrors.

In operation, the recorder 51 continues to record information such as the individual recordings 67-69, until a change in the information being recorded occurs. This is shown in FIG. 4 as the changes or breaks 86, 87 and 88 in the recordings 67-69. In the particular example shown, the recording proceeds with the records showing uniform operation of the device being monitored, in this case the school of fish 11. As shown in FIG. 4, the time that the breaks 86-88 occur on the three charts is not the same. Thus, the break '86 is shown at time t the break 87 is shown at time t and the break 88 is shown at time r,. The reason for this is the varying distances from the source of the signal, the school of fish 11, to the three ships 14, 13 and 15 which serve as the sources of the information from which the records 67-69 are made. As shown, signals received by ship 14 are represented by record 67, those received by ship 13 are represented by record 68, and those received by ship 15 are represented by record 69. Thus, since ship 14 is closest to the source 11, the sound signals from the source reach that ship first. On FIG. 4, the characters t t and t represent the times that the breaks" 86, 87 and '88 reach that ship first. On FIG. 4, the characters t t and t means of potentiometers which have their slide contacts connected to the knobs 75, 76, 77 and 78. To operate the bridge 54 to obtain electrical indications of the times the sound signals reach the ships 13, 14 and 15 from the source 11, the drive-means for the bridge 54 is energized so that the bridge moves with the record receiver 52. This locks the bridge 54 to records 67-69. While the bridge and the records are moving together, the knobs 75-77 are manipulated so that the plate 79 is moved outwardly from the bridge 54 until the hair line 85 which is carried by the respective supports 81, 82 and 83 is aligned with the same part of the breaks 86, 87 and 88. The amount of movement of the hair lines 85 necessary to align them with the breaks in their respective records is indicated on the counters 71, 72, 73 and 74 for the individual records. In addition, as the knobs 75-77 are manipulated, the slide contacts of the respective potentiometers, not shown in FIG. 4, are moved corresponding amounts. Thus, the amount of relative movement of each of the individual knobs 75-77 is immediately displaced on the counters 71-73 associated therewith, and the settings of potentiometers connected thereto are also related to that movement. Thus, the time arrivals of the sound from the source 11, as received by the ships 13-15, are translated by the bridge 54 and the equipment thereon into electrical quantities. The locking of the bridge 54 to the movement of the record receiver 52 gives the operator of the equipment suflicient time to accurately align the hair lines 85 with the breaks in the records. The operation of the overall system is explained in the copending application Ser. No. 514,525 of Michael Prebish, filed on Dec. 17, 1965.

In FIGS. 3, 4 and 5, the bridge 54 has been shown very schematically to provide an over-all picture without unduly cluttering the drawings. A more detailed showing of the bridge 54 is presented in FIG. 6. The bridge 54 comprises a base member 92 which carries at either end the drive pinions 91. The drive pinions 91 are connected by suitable drive shafts (not shown) to a motor 151 which is selectively energized by the operation of a toggle switch 152 mounted on a front panel 93. The bridge 54 also comprises a rear panel 94 and four stations 95, 96, 97 and 98. Adjacent the station 97 there is shown, in FIG. 6, an electrical connector block 99 for making suitable connection with outside equipment. Each station -98 comprises side walls 135 which contain appropriate gearing mounted therebetween. In addition, a zero set knob 134 and a hair line drive knob 101 are contained at each station. Each drive knob 101 controls, through the gearing which is shown in detail in FIGS. 7 and 8, the position of a carriage 127 moving in a guide 145 to drive a movable support 81 which carries the hair line 85 and a mirror 89 (not shown). A cover 153 fits over the entire bridge assembly to enclose it.

The construction of an individual station is shown in greater detail in FIGS. 7 and 8. The knob 101 contains a dial 102 and operates a counter 103 which is behind a window. The knob 101 is connected to a shaft 105 which drives a worm 104. A worm gear 107 mounted on a shaft 108 meshes with the worm 104 to drive a spur gear 111. A larger spur gear 112 meshes with the gear 111 and is mounted on a shaft 113 which has a spur gear 114 mounted on its other end. Meshing with the gear 114 is another spur gear 115 which drives a transducer 116. The gear 112 also drives a spur gear 121 which is connected to one input to a differential shown generally at 122. The other drive gear 123 is connected to another input to the differential 122 whose output is a shaft 124 on which is mounted a pinion 125. The pinion 125 meshes with a rack 126 which is mounted on the carriage 127. The gear drive 123 also meshes with a spur gear 131 connected to a worm gear 132 which meshes with a worm 133. The worm 133 is connected to the second knob 134. The side plate 135 provides bearings (not shown) for supporting the various gear shafts which constitute the assembly at each station. The carriage 127 is shown in greater detail in FIG. 8 and comprises three wheels; 141 at the rear, and 142 and 143 on cross members. The guide 145 serves to constrain and direct the movement of the carriage 127 which includes a forward portion 144.

The operation of the entire bridge assembly can be discussed at once with reference being made to FIGS. 6, 7 and 8. When an anomaly is detected in the recordings 67, 68 and 69, the switch 152 is placed in its on position to energize the bridge drive motor 151. This drive motor, through suitable drive means, causes the pinions 91 to rotate. If desired, the pinions 91 can be connected to the drive motor 151 through a drive linkage which includes a clutch so that the bridge 54 cannot be manually moved while the motor 151 is operating. However, the clutch permits the bridge 54 to be manually moved when the motor 151 is not energized. The pinions 91, as shown in FIG. 5, engage the rack 66 to drive the bridge 54 in synchronism with the movement of the record receiver 52. Once the bridge 54 is moving with the record receiver 52, the knobs 101 are manipulated individually. As a knob 101 is rotated, the scale 102 also rotates and the counter 103 behind the window is driven. The worm 104 rotates to drive the worm gear 107 and the shaft 108. As the shaft 108 turns, the gear 111 mounted on the shaft 108 drives a larger gear 112 mounted on the shaft 113. The shaft 113 also carries a gear 114 which is the same size as the gear 112. The gear 114 drives a gear 115 of similar size to cause the transducer 116 to rotate. The transducer 116 may be any mechanical-to-electrical transducer which able at the output connector 99. As mentioned above, the gear 111 is smaller than the gear 112 and there is a gear ratio between the worm 104 and the worm gear 107. In this manner, the appropriate gearing reduction between the rotation of the knob 101 and the subsequent rotation of the transducer 116 is achieved to produce an electrical output from the transducer 116 which bears a prescribed and suitable relation to the rotation of the knob 101 and to the values shown on the Vernier scale 102 and the counter 103. When this apparatus is used in connection with the system described in greater detail in the copending application of Michael Prebish, Ser. No. 514,525, the electrical output from the transducer 116 will bear a desired relationship to the distance that the carriage 127 is moved along the recording, and the figures shown on the counter 103 and the scale 102 will indicate the same relationship. Thus, each complete rotation of the knob 101 could show on the counter 103 a distance of, say, one nautical mile. At the same time, the electrical output from the transducer 116 would produce an electrical indication which would indicate a distance of one mile. The gearing ratio can, of course, be modified to accomplish particular ends. As the knob 101 is rotated, the gear 112 also meshes with the gear 121 to drive the differential 122. This produces rotation in the pinion 125 which causes the rack 126 to move, driving the carriage 127. Thus, as the knob 101 is rotated, a numerical indication of the amount of rotation is produced on the counter 103 and the scale 102, an electrical indication of the amount of rotation is produced at the output of the transducer 116, and the carriage 127 is moved an appropriate amount. The operation of the gearing is such that rotation of the knob 101 in opposite directions will produce opposite results in all three of these outputs in each station.

The carriage 127 is so constructed that it rests on the base member 92 and rolls across its surface on the wheels 141, 142 and 143. To ensure straight movement, the carriage member 127 moves through at least one guide 145 which is conveniently attached to an appropriate portion of the recorder 51. The forward portion 144 of the carriage 127 carries the movable member 81 and the hair line 85. Thus, as a particular knob 101 is rotated, the hair line 85 moves, either forward or backward depending upon the direction of the rotation of the knob. When the hair line 85 has been aligned with the anomaly on the recording over which its particular hair line 85 is mounted, the knob 101 is locked by the lock 106. This procedure is not absolutely necessary since the use of the worm 104 and the worm gear 107 tends to eliminate the possible reverse movement of the knob 101 by other means in the system, but in many cases locking the knob 101 may be desirable as an additional safeguard. The same operation is then performed for each of the other stations to align their hair lines 85 with the anomaly on their particular recordings. The electrical outputs from the transducers 116 are connected by appropriate wiring, not shown, to the output connector 99 for application to other equipment as shown in FIG. 3. In addition, the amount of movement of the hair lines 85 accomplished by the rotation of the knob 101 for each of the stations 94-98 can be directly read from the counter 103 and the scale 102 so that the actual distances between the various sources of information for the recordings 67, 68 and 69 can be directly determined.

Initially, at the beginning of each periods use, the entire bridge assembly should be zeroed to compensate for any variations due to wear, temperature changes, misalignment, etc. This zeroing is accomplished by the rotation of the knob 134 which drives the worm 133 to rotate the worm gear 132. The worm gear 132 drives a gear 131 to drive the drive gear 123 of the drive differential 122. This causes rotation of the shaft 124 and the pinion 125 to cause the carriage 127 to move. However, because of the use of the worm 104 and the worm gear 107, as well as the lock 106, rotation of the knob 134 will cause movement of the carriage 127 only, without causing corresponding movement of the transducer 116. Thus, with the electrical output of each station set at zero, the hair line of each station can also be set at zero so that the hair lines of the four stations shown on the bridge 54 and the electricaI outputs of these four stations may all initially be set to zero. Similarly, the use of the worm 133 and the worm gear 132 permits operation of the knob 101 without causing rotation of the knob 134 and corresponding slippage in the system.

Of course, the mechanisms shown in FIGS. 6, 7 and 8 are but one way of achieving the desired results. There are other ways, also. As explained above, a desirable gear ratio must be achieved between the rotation of the knobs 101 and 134 and the corresponding movement of the carriage 127 and of the rotation of the transducer 116. FIG. 7 shows a system which utilizes worms and worm gears to achieve this gear ratio and also to provide against reverse movement. However, spur gears could be used throughout, and locks such as lock 106 can be provided for the two knobs 101 and 134. A differential 132 has been used to separate the movements of the knobs 134 and 101 while providing for each knob to cause proper movement of the carriage 127. In addition, the pinion 91 and the rack 66 can be modified to provide a more positive drive with less danger of twisting of the bridge 54. For example, the rack 66 could have substituted for it a'cylindrical rack with its cylindrical portion riding in spaced V-wheels. The V-wheels serve as guide members for the rack and if pairs of such wheels are used at the spaced positions, they may also include individual adjustment means for aligning the bridge 54 at any time. Four stations are shown on the bridge 54, but it should be obvious that any suitable number of stations may be used. As shown, the zero adjust knobs 134 are located at the rear side of the bridge 54 and the initial adjustment knobs 101 are located in the front panel. Both knobs may be located on the same panel if desired.

As mentioned above, it is realized that the above specification may indicate to those in the art additional Ways in which the principles of this invention may be utilized without departing from its spirit.

What is claimed is: I

1. Converter apparatus for converting spaced information contained on a plurality of recordings into electrical and numerical information, said apparatus comprising a base, a plurality of stations aligned on said base with each other, each station being associated with an individual recording and each station including an indicator, means for moving the indicator at each station from its home position to a selected point on its associated recording, and means for converting the distance through which each of said indicators moves into electrical and numerical information.

2. The apparatus defined in claim 1 wherein said means for moving said indicator includes manual means.

3. The apparatus defined in claim 1 wherein said means for moving said indicator includes automatic means.

4. The apparatus defined in claim 1 wherein the home positions of all of said indicators are in a straight line, wherein said recordings are aligned, and wherein the straight line formed by the home positions of said i11- dicators is parallel to a line made by the zero positions on said recordings.

5. The apparatus defined in claim 1 wherein said converter means includes a scale calibrated in appropriate distances, means for indicating on said scale the amount of movement of said indicator, and means for connecting said scale indicator with said indicator so that they move in synchronism.

6. The apparatus defined in claim 5 wherein said converter means includes a device having a positionable member and generating an electrical signal proportional to the position of said positionable member, and means for connecting said positionable member to said indicator so that they move in synchronism.

7. The apparatus defined in claim 6 including means for placing said positionable member in its zero position, and means for moving said indicator to its home position without disturbing the position of said positionable member.

8. The apparatus defined in claim 1 wherein said converter means includes a positionable member, a device for generating an electrical signal proportional to the position of said positionable member, and means for moving said positionable member in synchronism with the movement of said indicator.

9. The apparatus defined in claim 1 wherein said recordings are moved together and further including means for selectively moving said base and said plurality of stations in synchronism with and in the same direction as the movement of said recordings to maintain a fixed relationship between said recordings and said base during the movement of said indicators.

10. Apparatus for indicating the relative positions of the same points which occur on several recordings which are aligned in side-by-side relation, said apparatus comprising a base, said base having a plurality of aligned stations supported thereon, each of said stations ineluding an indicator, means at each station for moving its indicator from a home position to a desired relationship with a point on the recording associated with it, the points on said recordings being the same, each station further including first converter means including a scale and a device for indicating selected portions of said scale, second converter means including a positionable member and a device for generating an electrical signal proportional to the position of said member, and means connecting said indicating device and said positionable member to said means for moving the indicator for converting the distance through which said indicator moves into electrical and numerical information.

References Cited UNITED STATES PATENTS 2,144,812 1/1939 Rieber. 2,243,730 5/ 1941 Ellis. 3,089,243 5/ 1963 Gerber. 3,184,848 5/ 1965 Lawrence.

WILLIAM D. MARTIN, JR., Primary Examiner US. Cl. X.R. 

